The present invention relates in general to terminals for high power automotive fuses and electrical connectors, and, more specifically, to a scalable terminal design for adjusting current-carrying capacity.
High-power fuse assemblies for power distribution boxes used in automotive vehicles commonly include a fuse body with a nonconductive housing encasing a conductive set of female terminals. The set of female terminals are each connected to a respective end of a fuse element retained in the housing. The female terminals are inserted over a set of male blade terminals extending from a power distribution box for completing an electrical circuit. The female terminals are typically designed with a spring-type feature to maintain a strong electrical contact with the male terminal blades. If the current flow in the electrical circuit increases above a predetermined current threshold, the fuse element will open, thereby terminating current flow across the respective set of female terminals. Spring-type female terminals are also used for other types of connections to male blade terminals, such as a connection from a wiring harness to an electrical device.
Copper has good electrical conductivity properties, and has been a preferred material for the terminals. However, copper is susceptible to relaxation (i.e., loss of spring force) as the temperature increases. Since temperature of the terminals increases as the current drawn in the electrical circuit increases, copper terminals have a reduced ability to maintain strong clamping force onto the male terminal blades. Relaxation of the female terminals decreases the overall contact area with the male blades, resulting in reduced electrical conductivity, increased resistance, and a further increase in temperature.
It is desirable to keep the overall size of an electrical distribution box or other connectors as small as possible while still providing the necessary current-carrying capacity. For any particular size of a fuse, the thickness and width of the female terminals is correspondingly limited. Therefore, the spring force cannot be further increased by simply making the terminals thicker or wider. When copper is used, the size limitations may make the desired spring force unattainable. Consequently, copper alloys for which relaxation does not occur until higher temperatures are reached have been used. On the other hand, copper alloys typically have a lower conductivity. For any particular size (i.e., volume) of fuse, the current capacity is thus reduced. In automotive applications, fuses using copper alloys are typically limited to 60 amps or less.
Commonly assigned U.S. Pat. No. 7,595,715 discloses an improved terminal system wherein a high conductivity material with a relatively low relaxation temperature (e.g., copper) is used for the current-carrying legs of a female terminal while a separate spring element with a relatively high relaxation temperature clamps the legs to the male terminal blades. It would be desirable to further increase current carrying capacity and to simplify design and development of female terminals employing legs and spring elements.